I really like dweste's idea of disappearing a team member half way though the exercise.

Here are some other ideas:
-for the person(s) that your searching for, have them spend a night out before the search begins. You will get a bit closer to realism for the search party (at least for the victim(s) - if they aren't savy outdoors!!!). This is for the junior of the team ;-)
-adding an injury to one or more of your team members through the exercise (i.e. broken leg, etc), which affects the numbers searching.
-add another search victim somewhere/anytime through the exercise, like the victim's young son/daughter
-loosing communications? Not sure about this, does it ever happen?

Just ideas, and not sure if any are appropriate.
Kris

I should read everything before posting!!! I just read NightHiker's post and some common points. Sorry man.